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Author

Reyes, Catherine

Abstract

In this thesis, electrospun nanofibrous membranes for capturing submicron particles from simulated exhaled breath are investigated. Although it is known that aerosols of Influenza are responsible for increased rates of infection, studies have yet to succeed in quantifying sub-micron Influenza particles present in contagious exhaled breath. Therefore, here we observe the extent to which airborne sub-micron particles, modelling the size, and surface charge of exhaled viral particles, can be captured by electrospun Nylon-6 nanofiber media. An aerosol of salt particles was generated from an aqueous sodium chloride solution. This solution modeled an exhaled Influenza type aerosol because the majority of droplet sizes ranged from 0.52[MICRO SIGN]m to 4.0[MICRO SIGN]m; the typical size range of aqueous droplets in exhaled saliva. A large animal respirator simulated the process of human breathing. During exhalation, the respirator dispersed the salt aerosol to nanofiber membranes for capture. The Nylon-6 membranes used in this study were uniformly electrospun on a large scale [15cm by 96cm] with targeted fiber diameters ranging from 100 nm to 200 nm. FESEM (Field Emission Scanning Electron Microscopy) and EDX (Energy Dispersive X-Ray Spectroscopy) were used to show that these membranes captured salt particles ranging from 30nm - 200nm (the viral particle size range reported most difficult to isolate). Nylon-6 nanofiber membranes could overall capture up to 39% higher salt aerosol concentrations than the control membranes, and did not break during the test process. BET (BrunauerEmmett-Teller) and porometry analysis of the electrospun membranes show that small pore sizes (104nm - 122nm) and high surface areas (44m2/g - 58m2/g) contribute to better aerosol capture than for the control membranes. Furthermore, a cascade impactor was employed to quantify the changes in salt capture before and after the nanofiber filter membrane was using in the breathing apparatus. Compared to the control membranes, the highest percent of smallest sized aerosol droplets, between 0.52 m - 1.55 m, can be captured by all types of electrospun membranes. Additionally, to increase hydrophilicity of the Nylon-6 membranes, poly(acrylic acid) was grafted to the Nylon-6 membrane by two methods. In the first method, poly(acrylic acid) was grafted onto the chain-end surfaces of the Nylon-6 electrospun membrane using the amine-to-carboxylic acid coupling agent: EDC (1-ethyl-3-(3dimethylaminopropyl)carbodiimide hydrochloride). For the second method, the electrospun membranes were mutually gamma irradiated in an acrylic acid monomer solution to initiate free radical polymerization grafting. The second method resulted in high add-on of acrylic acid in the form of monodisperse beads on the surface. Found via FTIR (Fourier Transform Infrared) analysis, there is 17% - 20% chance of grafting occurring, with up to a 9% overall weight increase in the membranes. The crystalline structure of the Nylon-6 is also significantly modified in the process, with higher Hm values. Overall surface area, porosity, and mechanical properties of the membranes decreased, and the salt particle capture did not improve, however. The end use goal for the plain and surface modified nanofiber membranes is that they can serve as effective wearable textile materials to supplement the capture, and characterization, of aerosol-driven nanoscale infectious particles exhaled from human breath.